Gunmen wearing suicide vests attacked government targets in the Kurdish-controlled city of Kirkuk and killed 16 at an Iranian-run construction site further north on Friday as troops advanced on jihadist bastion Mosul.

American forces are trying to relieve pressure on Iraqi forces at the geographically important Baiji oil refinery, hitting militants with 26 air strikes since Tuesday and helping drop 18 pallets of supplies, the top U.S. general said on Thursday.